1. Field of the Invention
This invention relates to air filtration, and more particularly to a universal air filter kit having a telescopically adjustable gasketed frame for residential and light commercial applications.
2. Description of the Prior Art
The use of air filters to remove particulates from an air stream is well known in the art. Air filtration is primarily used in both commercial and residential heating, ventilating, and air conditioning systems for removing atmospheric dust, or other undesirable airborne matter.
Atmospheric dust comprises a complex mixture of smoke, fumes, dry granular particles, and fibers. These components and their concentrations vary with the geography of the locality (urban or rural), the season of the year, weather, the direction and strength of the wind, and the proximity of dust sources. A sample of atmospheric dust usually contains soot and smoke, silica, clay, decayed animal and vegetable matter, organic materials in the form of lint and plant fibers, and metallic fragments. It may also contain living organisms, such as mold spores, bacteria, and plant pollens, which may cause diseases or allergic responses.
Particles in the atmosphere range in size from less than 0.01 pica meters to the dimensions of lint, leaves, and insects. Particulate contamination indoors in influenced by smoking, human sources, human activities, and other sources such as equipment, furnishings and pets.
Different filtration applications require different degrees of air filtration. In industrial ventilation, it may only be necessary to remove the coarser dust particles from the airstream in order to insure the protection of mechanical equipment and cleanliness of the structure. A residential application, on the other hand, may require removal of even finer dust particles, often the worst offenders of home interior discoloration and indoor air quality problems. Electronic air cleaners or high efficiency media filters may be required for small particle removal, specifically the respirable fraction, which often just be controlled for health reasons.
The characteristics of airborne contaminants most affecting the performance of an air filter include particle specific gravity, concentration, electrical properties, and most importantly, size. Thus, the degree of air cleanliness required and contaminant concentration are major factors influencing filter design and selection.
Three operating characteristics distinguish the various types of air filters: efficiency, airflow resistance, and dust holding capacity. Efficiency measures the ability of an air filter to remove particulate matter from an airstream. Airflow resistance is the static pressure drop across the filter at a given airflow rate. Dust holding capacity defines the amount of a particular type of dust that an air cleaner can hold when it is operated at a specified airflow rate to some maximum resistance value or before its efficiency drops seriously as a result of the collected dust. Complete evaluation of an air filter thus requires data on all of the aforementioned factors.
The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has developed testing methods for determining air filter efficiency that have become standard in general ventilation applications in the United States. These testing techniques have been unified into a single test procedure, ASHRAE Standard 52-76, recently renamed as ASHRAE Standard 52.1-1992. In this procedure a known amount of standardized test dust is fed into a test filter at a known and controlled rate. The concentration of dust in the air leaving the filter is determined by then passing the entire airflow through a high efficiency after-filter and measuring the gain in filter weight, In the ASHRAE Standard 52.1-1992, Dust Holding Capacity Test, the same test dust is fed to the filter, and the pressure drop across the filter rises as dust is collected by the filter. The test is terminated when the pressure drop across the filter reaches the maximum operating resistance set by the manufacturer.
A variety of filter configurations known in the art are routinely tested and rated according to ASHRAE Standard 52.1-1992. Among these types of filters are panel filters, renewable media filters, and electronic or electrostatic air cleaners. Panel filters consist of viscous impingement filters and conventional dry type filters. Viscous impingement filters are panel filters where the filter media is coated with a viscous substance, such as oil, which adheres to particles that impinge on the fibers. Renewable media filters are found exclusively in commercial and industrial applications; while dry-type panel filters and to a lesser extent electronic air cleaners are primarily used in residential applications.
A common problem in the filtration industry relates to filter size requirements. Typically, air filters are mounted in a filter track. However, filter tracks of various sizes are used for mounting filters in a ducted air stream, or in an air handling apparatus. For example, common filter track dimensions include 12".times.20", 12".times.24", and 18".times.24". Furthermore, a wide variety of "non-standard" filter track dimensions are found in association with various systems. Accordingly, for any given filter track, it is important that the proper filter size be obtained and installed. If the filter is too large for a given track, installation may prove impossible without modifying either the filter, or the track, or both. On the other hand, if the filter is too small for a given track, large quantities of air may simply by-pass the filter.
U.S. Pat. No. 3,675,402, issued to Weed, discloses an adjustable filter assembly for a filter or the like which is telescopically adjustable in two different directions. The device disclosed by Weed, however, is designed for use in apertures of buildings such as windows or doors, and is not suitable for use as an adjustable filter frame in a ducted airstream. An example of one such disadvantage stems from Weed's failure to provide means for sealing the frame relative to the surrounding support structure for maintaining an seal around the filter.
Furthermore, most conventional air filter assemblies comprise a quantity of filter media having a light weight frame often made of cardboard. Since the media is often not securely fastened to the surrounding frame, a support grid or wire mesh is used on the leaving air side of the media to aid in supporting the media within when placed in a moving air stream. However, the support grid necessarily reduces the net free area of the filter effectively reducing the face area of the filter. As a result, the velocity of air flowing through the filter media increases, due to the effective reduction in free area, thereby decreasing filter performance and increasing the pressure drop across the filter. In addition, cardboard filter frames fail to provide a positive perimeter seal thereby allowing a substantial quantity of the airstream to by-pass the filter entirely.
Accordingly, there exists a need for a kit, for residential and light commercial use, having a telescopically adjustable filter frame capable of independent length and width adjustment, and which provides means for maintaining a positive perimeter seal when installed in a filter track. Such a kit would enable a user to adjust the frame to the size required to fit the user's filter track, and install a quantity of filter media therein without requiring the use of a net free area reducing support grid.
It is to providing this, and other, needs that the instant invention is directed.